Just write on his nichirin sword.

Kaiyochi is a young man of average height with dark brown eyes and medium indigo hair. He sports a Demon Slayer uniform that includes loose hakama pants and a dark blue haori, which ends in a light red shade at the bottom. His Nichirin Sword and its sheath are both indigo and dark red, secured under his belt. He completes his ensemble with black tabi socks and blue zōri over them. During his encounter with Yotsuyahi, the Upper Rank Three, Kaiyochi awakened his Demon Slayer Mark. The mark, which he acquired despite Yotsuyahi's escape, features a jet-black sun with yellow and purple star-like dots and and a supernova-like border, all located on the left side of his forehead.

Kaiyochi's Nichirin Sword holds the same design as his usual attire. The handle is wrapped in a rich indigo cloth, boasting a diamond pattern engraved upon it, and the guard is studded with dark red gemstones and adorned with intricate designs that mirror the dense weave of the night sky. These colors bleed into the blade itself, transitioning from a deep red at the base to a vivid indigo at the tip - a visual embodiment of the transition from night to dawn. The sheath, crafted flawlessly from a light, durable wood, carries these shades too; it is carefully lacquered in overlapping layers of indigo and dark red, resulting in a dual-tone color scheme that compliments the sword.

Etched into the blade is the unique inscription, written in an archaic script that only the Demon Slayers could decipher: '夜明けの始まり,' translating to 'Dawn's Beginning.' This serves as a constant reminder of Kaiyochi's resilience and unwavering commitment to vanquishing demons, symbolically vowing that each new dawn will be the beginning of hope for mankind.

Lastly, upon acquiring his Demon Slayer Mark, a new detail was added to his sword. Resembling the mark on his forehead, a sun-like emblem was engraved close to the hilt of his Nichirin sword. The golden and purple star-like dots scattered inside the sun mimic a galaxy of their own, and rounding the sun is a supernova-like border, signifying the limitless, explosive potential that lies within him.

To write on Kaiyochi's nichirin sword, you can follow these steps:

Step 1: Prepare the necessary materials
- Obtain a permanent marker or calligraphy pen with a color that contrasts well with the indigo and dark red colors of the sword.
- Make sure to have a clean cloth or tissue handy for any excess ink.

Step 2: Clean the sword
- Before writing on the sword, wipe it gently with a clean cloth or tissue to remove any dust or dirt. This step ensures that the ink adheres properly to the surface.

Step 3: Plan the design
- Decide on the specific words, symbols, or design you want to write on the sword. Consider the available space and how it will complement Kaiyochi's overall appearance.

Step 4: Test on a small area
- Before committing to writing on the sword, you may want to test the marker or pen on a small, inconspicuous area to ensure the ink does not bleed or smear.

Step 5: Begin writing
- Start by applying gentle and consistent pressure on the marker or pen.
- Carefully write the desired words or draw the chosen design on the sword, following the shape and contours of the blade or sheath.
- Take your time and make steady strokes to achieve the desired result.

Step 6: Allow the ink to dry
- After completing the inscription, give the ink some time to dry completely. This will prevent smudging or smearing.

Step 7: Check for any touch-ups
- Examine the written inscription to see if any parts need touch-ups or additional details. Use the permanent marker or pen to correct any imperfections, if necessary.

Step 8: Final check and display
- Once the ink is fully dry and any touch-ups have been made, examine the writing one last time to ensure it meets your expectations.
- Display the nichirin sword in a safe and secure location, where it can be admired as a unique feature of Kaiyochi's Demon Slayer ensemble.